The present invention generally relates to a full-size image sensor, and particularly to a full-size line sensor which can be applied to an optical reader provided in a facsimile machine, a digital copier, a handy scanner and so on.
FIG.1 is a cross sectional view of a conventional total contact type full-size image sensor (see Japanese Patent Publication No. 58-14073 or 58-46182, or U.S. Pat. No. 4,805,032). Referring to FIG.1, light emitted from a light source (not shown) passes through a window W formed in a light interrupting layer 2 mounted on a substrate 8, and then passes through a transparent protection layer 3 so as to cover photoelectric conversion elements 1 arranged into a line. Then, the light is projected onto a document 5, which is fed by a platen roller 4, and is reflected thereon. The quantity of the reflected light is based on image information formed on the document 5. The reflected light passes through the transparent protection layer 3 and is projected onto the photoelectric conversion elements 1, which convert the received light into corresponding electric signals.
The image sensor shown in FIG.1 does not require a full-size imaging element such as a selfoc lens array (SLA). In view of this point, the efficiency in use of light is high and thus a high signal-to-noise ratio can be obtained.
However, the document 5 pressed by the platen roller 4 slides directly on the transparent protection cover 3. This causes a flaw on the surface of the transparent protection cover 3. Further, the transparent protection cover 3 may be worn away over a long period of time. The occurrence of flaw or wear affects the incident light or the reflected light. As a result, time deterioration of S/N ratio and resolution is caused. Moreover, the following disadvantage is presented when an external integrated circuit chip 7 serving as a peripheral circuit (drive circuit) for the photoelectric conversion elements 1 is used together with the image sensor. In this case, the substrate 8 is necessary to have a width sufficient to prevent bonding wires 6 for connecting bonding pads (not shown) formed on the substrate 8 and the integrated circuit chip 7 from coming into contact with the platen roller 4 or the document 5. In order to reduce the size of the substrate 8, it is conceivable that each photoelectric conversion element is formed as small as possible. However, a reduced photoelectric conversion element is affected by static electricity. This increases noise or causes a malfunction of the peripheral circuit (drive circuit) formed in the integrated circuit chip 7.